Steel melting furnace and process of manufacturing the same



March 15, 1932. A SPRENGER 1,849,441

STEEL MELTING FURNACE AND PROCESS OF MANUFACTURING THE SAME Filed Nov. 10, 1928 n wen/or 15 bility of the same.

Patented Mar. 15, 1932 UNITED STATES PATENT OFFICE I ARTHUR SPRENGER, OF BERLIN, GERMANY STEEL MELTING FURNACE AND PROCESS OF MANUFACTURING THE SAME Application filed November 10, 1928, Serial No. 318,550, and in Germany November 29, 1927.

A serious inconvenience connected with the furnaces used for the production of steel is their short life. The liquid molten material in combination with the high temperature are the reason that, after a short time ofservice already, the walls of the steel smelting furnace are so attacked that they have to be renewed. The short duration of steel smelting furnaces is very disturbing for the production not to mention the considerable expenses caused thereby. Repeated attempts have been made to discover a material which is suitable for the production of steel smelting furnaces or adapted to increase the dura- These attempts have however not given satisfactory results. This relates specially to furnaces in which steel alloys possessing a high melting point have to be produced and also to so called hot going furnaces.

This invention makes it possible to produce steel smelting furnaces possessing very great resisting capability against the actions of the hot liquid molten material, i. e. long lasting furnaces. The steel smelting furnace according to the invention is characterized in that the walls as carrying elements contain masses, which consist mainly of chromium-magnesium and aluminum combinations and have been obtained by (smelting at high temperatures.

It was a surprise to find that a mass, to be obtained for instance by melting together chromic oxide, magnesium oxide and aluminum oxide or of minerals or masses containing these substances, is distinguished not only by specially high refractoriness but also by stableness at extremely high temperatures and by extraordinary resistance against chemical actions of any kind. The proportion of the several constituents, chromium, magnesium and aluminum, may be variable; condition is however that in the finished mass the oxides of these elements form the main constituent for instance 75% and more. It is advisable to keep the percentage of magnesium oxide not below 15% and the percentage of alumina not below 20%.

The initial materials are, as stated above,

molten together, i. e. transformed into a castable mass, by treatment at high temperature. From this castable liquid mass the walls of the steel smelting furnace can be made either by direct casting in suitable moulds, the casting being carried out directly at the place where the furnace has to be erected, so that the solidified mass forms the wall of the furnace without having to be transported, or the elements of the furnace-are cast in suitable moulds at any desired place and the furnace is put together from these elements, or the mass is first solidified and then cut into convenient pieces to be used for building up the furnace walls. In the latter case care has to be taken to fill the remaining joints and hollow spaces.

VVnen directly casting of the molten material the entire furnace is, so to say, cast of a piece. When the furnace is built up from several elements binding agents may preferably be used for ensuring adhering of the several elements.

The first form, the productionof the furnace by casting in a piece, is specially practical. For carrying out this method -Sl16&tl1 7 ing walls have to be erected, between which the molten mass consisting of chromium, magnesium and aluminum combinations is cast. For erecting these sheathing walls a refractory material will bepreferably used and in first instance such a material which as regards composition is similar to that ofthe moltenmaterial. In this manner it is not necessary to remove the sheathing walls as they unite solidly with the molten mass and form one piece with the same. With this on jectin View it is advisable that the material used for erecting the sheathing walls does not contain foreign bodies which reduce the refractoriness or influence in generalthe good propertiesof the molten mass. For erecting these sheathing walls chromite brick have proved specially adapted-asat the casting of the hot liquid molten mass they partly-dis solve in this molten mass, possessing however nevertheless such stability that they support. the molten material during casting it in place. Thecasting ofa furnace is carried out for instance in the following manner Referring to the drawings, Figure 1 is aveitical longitudinal section; Figure 2 a vertical cross section and Figure 3 a horizontal section of furnace embodying my invention.

The furnace to be cast consists essentially of four walls, a bottom and a roof; it resembles in outer shape a long large box resting upon two concrete columns.

On the cast iron plate a a rolled layer preferably of chromite stones Z2 is built. On this pavement thin walls 0 approximately mms. wide and also of chromite stones are built only one half stone high up to the dotted line (Z(Z. The channel formed in this manner is then filled with hot liquicmaterial by distributing the contents of an electric furnace for instance over the distance ec, then over the distance e then over the distance fg and so forth. If in this manner a complete ring has been formed, the thin walls c-0 of chromite stones are built higher and the channels formed are filled by casting in the manner just described. At the door posts it the walls are built several layers high in order that the posts may be completeo in 1 or 2 castings. In order to cast the vault m a scaffolding is built in the furnace chamber and on this scaffolding a fiat layer Z of chromite stones is placed, whereupon the vault is cast over this layer. This can be carried out layer-wise or zone-wise.

The bottom of the hearth can be cast at th same time that the boundary walls of the hearth are erected, up to the height of the fore plate. It might however be cast subsc quently into the furnace prior to the completion of the vault.

WVith this object in view the longitudinal side walls are tapered towards the foundation plates, as indicated at 2'. In the longitudinal direction the hearth chamber is subdivided by a number of walls Fig. 1 of differ ent heights, and the sections thus produced are filled by casting. In this manner the hearth obtains in longitudinal section adopts a concave shape, while it is possible to give to the same in cross section at the height of tl e pouring level an inclination according to the line 0, which towards the head end of the fun nace merges gradually into the horizontal plane a. In this manner one obtains a hearth with large mould which cannot lift.

As soon as the furnace has been cast in the manner described the fittings are inserted and the service can begin. The fittings are constructed so that, as far as they extend from the bottom plates up to the height of the fore plates, they need not be removed for repair, as a repairing of the hearths is scarcely necessary in a form of construction as described and, if it should become necessary,it can be carried out without the fittings between bottom plates and the height of the fore plate impeding the repairing.

The remaining anchorage is of iron construction in such a manner that any such longitudinal anchoring wall or end wall can be lifted off the crane in one operation, so that a taking to pieces and putting together of the fittings for carrying out the repairs requires little time and expense.

The building up of the thin chromite walls 0 is carried out preferably with rapidly binding mortar, like cement, water glass and the like. When casting of the mass the chromite stones will naturally partly crack and burst, which can be somewhat moderated by the use of very coarse-grained chromite stones. This bursting and cracking of the stones is immaterial, as the hot liquid molten mass will weld everything together. The chromite walls fulfill further the following purpose The outer walls serve for insulating. The inner walls serve to ensure, that, when the heating of the furnaces is started, the cast walls are only quite slowly heated to the required temperature. Bursting off of the cast refractory walls is thereby prevented.

The inner chromite walls will, during the first weeks of service, gradually be eroded and slagged ofl'. Cracks and fissures in "the cast walls will however be perfectly welded at this occasion so that the slag cannot penetrate into the cast wall material, this being essential for resistance and durability of these elements against destruction by slag.

The walls of the steel smelting furnace, instead of being cast from the molten material, may be put together from elements obtained by solidifying of the molten material, for instance in such a manner that larger plates, bricks, moulded bodies of any kind and the like are produced and then joined in a manner known per se. It is however more practical not to produce moulded furnace elements, but to break the solidified molten ma terial into pieces, to build up from these pieces the furnace wall in such a manner that it is self-supporting, and to fill during or after the erection of the wall the hollow spaces by a backing of a less refractory material. This packing or backing of the hollow spaces may be carried out for instance by casting with a mass at disposal in molten state, for instance chromite iron stone, magnesite or the like, but it may be carried out by ramming with an accordingly crushed mass. Also the outer surface of the wall will then be smoothed eventually by ramming on an appropriate mass. But for the ramming or backing such a material will be preferably selected which itself is capable of binding, in order to ensure without heat treatment already a certain resistance of the wall. As appropriate substances magnesia, alumina ce-' ment, eventually with addition of other highly refractory substances, as corundum, silicon carbide, chromium containing masses and the likevmaybe mentioned. Under certain conditions the filling mass may contain organic or inorganic binding substances. I

It is not necessary to use for the preparation of the filling mass exclusively substances which are stable at the high temperatures in question, as the material which withstands the thermical and mechanical stresses, holds the wall and the less refractory filling material may eventually soften without any danger for the working of the furnace.

It is of special advantage that the thickness of the boundary walls may be considerably less thick than in the commonly used steel smelting furnaces, a thickness of the walls of chromite stones of 65 mms. and of the cast walls of 250 mms. is quite sufficient. Another advantage consists further in that the material of the furnaces can be used again, immaterial whether metal slag adheres to it or not. If the material of the walls of a furnace to be dismounted is free from slags, this material can be filled in pieces directly between the sheathing walls and cast together with molten material or can be used to form new walls in the manner above described. If it is however interspersed with slag, the material in pieces will be charged into the smelting furnace, which at the smelting treatment the metal separates from the less refractory slag substances by segregation.

It has been proposed, to heat smelting furnaces with coal dust. The experiments have however not been successful up to the present, as it has not been possible to make the masonry sufliciently resistant against the actions of the steel slag and of the fuel ashes. This problem is solved by the present invention, as the material from which steel smelting furnaces have to be made, i. e. a mass which consists mainly of chromium, magnesium and aluminum combinations and which has been obtained by treatment at high temperatures, possesses such refractoriness and at the same time also resistance against chemical actions of any kind, that it is possible to heat a steel smelting furnace with coal dust.

A furnace fitted with coal dust burners and built according to the invention can be operated in the usual manner with regenerators, for. instance after the Siemens regenerative system. In this case it is advisable to make also the trellis-work of the regenerators of the same highly refractory material.

The present invention is a considerable improvement of the building of steel smelting furnaces. When working according to the invention it is possible to produce furnaces possessing specially long duration and at the same time the economy of the steel smelting process is considerably increased.

I claim I 1. A steel melting furnace having cast walls of a molten mixture containing at least of the oxides of chromium, magnesium and aluminum.

2. A steel melting furnace having walls built of cast elements consisting mainly of chromium, magnesium and aluminum oxides.

3. The method of making steel melting furnaces, which comprises forming a mold of highly refractory sheathing and pouring into said mold a molten refractory mixture containing mainly oxides of chromium, magnesium and aluminum.

4. A method of making steel melting furnaces which comprises forming a mold of highly refractory material similar to that of the furnace wall and pouring into said mold a melt containing at least 75% of oxides of aluminum, magnesium and chromium, the mold becoming fused to the furnace wall.

5. A method of making steel melting furnaces, which comprises building a mold of chromite brick and pouring into the mold a melt consisting mainly of alumium, magnesium and chromium oxide, to which the mold becomes fused.

6. A method of building steel melting furnaces, which consists of building the walls of a fused mass comprising at least 75% of the oxides of aluminum, chromium and magnesium, and backing the built walls and packing them with a less refractory material.

7 A method of building steel melting furnaces, which consists in building the walls of a fused refractory containing at least 75% of the oxides of aluminum, magnesium and chromium, and backing and packing the walls with a fused material of less refractory properties.

8. A method of building steel melting furnaces, which consists of forming the walls of a fused refractory comprising at least 75% of the oxides of aluminum, magnesium and chromium, and backing and packing the wall with a mass containing an inorganic binder.

9. A furnace for smelting steel having its hearth, side walls and roof cast of a refractory containing at least 75% of the oxides of chromium, magnesium and aluminum fused together. V

10. A steel'melting furnace having walls of a fused material containing oxides of chromium, magnesium and aluminum to at least 75%, said walls being sufficiently mechanically resistant to carry the parts of the furnace resting thereon and the fittings.

In testimony that I claim the foregoing as my invention, I have signed my name.

ARTHUR SPRENGER. 

